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Certain species of predatory insect trap their prey, e.g. the ant-lion larva.
Summary of Section 2.5
The wings of all orders of flying insect appear to be derived from a common
ancestral form. It is possible that development of wings led to the enormous
diversity of insect species that are found today.
Summary of Section 2.6
Insect flight requires a large amount of energy; ATP is produced in the
mitochondria within the flight muscles, but most of the energy released by
breakdown of fuel is dissipated as heat.
Summary of Section 2.6
Contractions of the flight muscles generate heat within the thorax; large
flying insects such as dragonflies and bees may be at risk of overheating
during flight.
Summary of Section 2.6
Wing-beat frequencies vary in different species, as do flying speeds.
Summary of Section 2.6
There are two types of flight muscle, direct and indirect, which produce wing
movements by different means. The direct muscles are older in evolutionary
terms than the indirect muscles.
Summary of Section 2.6
The neural control of flight has been studied in the locust. A central pattern
generator of interneurons controls the basic flight pattern, which is modified
by flight interneurons in response to external conditions detected by
sense organs.
Summary of Section 2.6
Where two organisms have some form of association in their life cycles
evolution can act upon them in a reciprocal fashion. This phenomenon is known
as coevolution.
Summary of Section 2.7
Coevolution is well illustrated by some flowering plants, which appear to have
coevolved with their insect pollinators, particularly the heliconids and the fig
Summary of Section 2.7
Coevolution is often a feature of parasites and hosts.
Summary of Section 2.7
Helminth parasites include the flukes and tapeworms (Platyhelminthes), the
roundworms (Nematoda) and spiny-headed worms (Acanthocephala).
Summary of Section 3.2
Monogenean flukes with direct life cycles are ectoparasites of vertebrates.
Digenean flukes, which may have one or more intermediate hosts between
the molluscan primary host and the vertebrate definitive host, are
Summary of Section 3.2
Blood flukes show extreme adaptation of morphology and adaptive responses
to the immune system of their hosts.
Summary of Section 3.2
Tapeworms with indirect life cycles occur in the gut and are characterized by
having a scolex with suckers and hooks and a segmented body with repeating
units or proglottids, the sexually mature in the middle and the gravid at the
end. They occur in the gut.
Summary of Section 3.2
Roundworms may have direct or indirect life cycles.
Summary of Section 3.2
Parasitic arthropods range from the highly modified forms such as the
pentastomids and Sacculina to those which barely differ from free-living
Summary of Section 3.2
Fleas, lice, mites and ticks are ectoparasites, relatively unmodified compared
with their free-living relatives, and often act as vectors of disease-causing
Summary of Section 3.2
Parasitoids are insect larvae which always kill their host by feeding on its
internal tissues.
Summary of Section 3.2
A few gastropod molluscs are ecto- or endoparasites.
Summary of Section 3.2
Internal parasites often take up nutrients across the body wall. The tegument
is important in absorption in tapeworms and in flukes, particularly for the
larval stages in molluscan hosts.
Summary of Section 3.3
Roundworms (nematodes) have a gut and, with very few exceptions, cannot
absorb nutrients through the cuticle of the body wall.
Summary of Section 3.3
Parasites are known to induce anorexia in their hosts which may be a
consequence of the host’s immune response or help the parasite to maintain
its infection.
Summary of Section 3.3
Platyhelminth parasites probably arose from free-living ancestors in the
oceanic ooze.
Summary of Section 3.4
Those attaching to the external surface of fish became monogenean parasites.
Summary of Section 3.4
Those invading the gut of molluscs evolved into digenean parasites.
Summary of Section 3.4
The likely ancestors of tapeworms were monogeneans which invaded the
cloaca and then the intestine of fish.
Summary of Section 3.4
Both parasite and host evolve together in stepwise fashion, i.e. coevolution.
Summary of Section 3.4
The evolution of sexual reproduction, which enhances variation, may have
been a response to parasitism.
Summary of Section 3.4
Parasites often induce morphological or behavioural changes in their hosts
that enhance their chances of transmission to the next host.
Summary of Section 3.4
The chordate body plan includes a tubular nerve cord dorsal to a central
notochord, and the pharynx perforated to form gill slits. The dorsal
musculature, muscles and nerve cord are segmented. A ventral heart pumps
blood through the gills and the rest of the body.
Summary of Section 4.2
Vertebrates are the most abundant and diverse of three subphyla of chordates.
The other groups are mostly marine filter-feeders with numerous gill slits.
Summary of Section 4.2
Primitive jawless vertebrates have seven pairs of pharyngeal gill slits each
supported by a skeletal tissue that forms the gill arch. The two anterior arches
form the jaws and their attachment to the braincase in other fishes, leaving
five functional pairs of gills. Gills disappear entirely in terrestrial vertebrates.
Summary of Section 4.2
Vertebrate blood is contained entirely within vessels and is pumped around
the body under pressure. Mechanical properties of the walls of the larger
vessels accommodate changes in pressure generated by the pumping heart
and prevent bursting and excess bleeding.
Summary of Section 4.3
Gas exchange and nutrient transfer take place at the capillaries that permeate
all cellular tissues.
Summary of Section 4.3
The blood of almost all vertebrates contains the pigment haemoglobin, which
is of lower molecular weight than that of most invertebrate haemoglobin, and
is confined inside erythrocytes. It binds oxygen and (to a different part of the
molecule) carbon dioxide.
Summary of Section 4.3
The numerous cells make vertebrate blood rather more viscous than
invertebrate blood. The composition of the blood, including the size and
abundance of erythrocytes, differs greatly between species and changes
during the life cycle.
Summary of Section 4.3
Haemoglobin binds more strongly to oxygen at higher pH and releases it
more readily at lower pH. This Bohr effect, and the shape of the oxygen
dissociation curve, arise from changes in the molecular configuration of the
pigment — and hence its capacity to bind oxygen — with pH.
Summary of Section 4.3
The Bohr effect determines the efficiency of delivery of oxygen from the
respiratory surface to the tissues that utilize it. Metabolic activity increases
the acidity in the tissues, which releases oxygen from the haemoglobin.
Summary of Section 4.3
Haemoglobins of different species, and in some cases different stages in the
life history of the same species have oxygen dissociation curves and Bohr
effects that adapt them to their habits and habitats.
Summary of Section 4.3
Breathing is controlled by neurons that are acutely sensitive to the carbon
dioxide concentration of the blood.
Summary of Section 4.3
Structural tissues are particularly diverse and complex in vertebrates.
Summary of Section 4.4
Bone is a living tissue unique to the vertebrates; osteocytes are incorporated
into an extensive extracellular matrix of collagen fibres and nourished from
blood vessels that permeate the entire structure. Small crystals of
hydroxyapatite form in the extracellular matrix.
Summary of Section 4.4
Cells associated with bone continuously repair and remodel the hard
Summary of Section 4.4
Bone is dense and sinks in water; free-swimming bony fish have buoyancy
devices that enable them to float. The skeleton of chondrichthyan and certain
other (especially large) fishes is cartilage.
Summary of Section 4.4
Teeth are derived from bone. The main tissue, dentine, consists of a heavily
mineralized matrix with the cell bodies assembled in the pulp cavity.
Summary of Section 4.4
Most vertebrate teeth are replaced several times during life and in response to
breakage or wear. Mammalian teeth are more complex in structure and are
replaced only once or not at all, though most specialized herbivores have
some continuously growing teeth. Ivory is specialized to resist desiccation,
abrasion and impact.
Summary of Section 4.4
Skin consists of an inner living layer (the dermis) rich in extracellular
collagen. Terrestrial vertebrates also have an outer epidermal layer of dead,
keratinized cells that provide mechanical protection and limit permeability.
Skin contains glands that secrete mucus, sweat, pheromones and various
antimicrobial and anti-predator substances. Either layer may be pigmented.
Summary of Section 4.5
Mammary glands secrete milk that nourishes the young and these glands are
unique to mammals. They are derived from skin glands and the proteins in
milk and the enzymes involved in the synthesis of milk components are
similar to other vertebrate proteins that have different functions.
Summary of Section 4.5
In all modern amphibians (but not most extinct species) the dermal layer is
extensive and contains several large glands, but the epidermal layer is
reduced. The soft, moist skin serves as a respiratory surface.
Summary of Section 4.5
Feathers and hair are derived from the epidermis and consist almost entirely
of keratin, plus variable quantities of pigments.
Summary of Section 4.5
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